Process for producing an easily-slidable polyarylene thioether film

ABSTRACT

A process for producing an easily-slidable polyarylene thioether film having an arithmetic average surface roughness, Ra, in a range of 2-200 nm and a dynamic friction coefficient, μk, within a range of 0.1-0.6 at least on one surface of the film, which comprises: 
     a) contacting at least one surface of an amorphous film, containing the polyarylene thioether, consisting essentially of repeating units of the formula: ##STR1## with at least one organic solvent having a solubility parameter within a range of 8.5-11.5, and being selected from the group consisting of ethers, thioethers, organic amides, halogenated hydrocarbons, carbon disulfide, aromatic hydrocarbons, pyridines, quinolines, nitro compounds, ketones, esters, cyano compounds and sulfones; or a mixture of any of the above solvents with water, alcohols or aliphatic hydrocarbons; until the arithmetic surface roughness, Ra, of the contacted film reaches 10-150 nm, thereby increasing a degree of crystallization at the surface of the film which is higher than that of the inside; b) stretching the contacted film at a temperature within the range of 70-130° C. and at an area stretching factor of 4-18 times; and 
     c) heat setting the stretched film at a temperature within the range of 180°-280° C. for a time within a range of 1-2000 seconds.

This application is a continuation of application Ser. No. 07/120,834,filed on Nov. 16, 1987, now abandoned.

BACKGROUND OF THE INVENTION

The present invention concerns an easily-slidable polyarylene thioetherfilm not containing a substantial amount of powdery lubricant, as wellas a production process therefor.

Specifically, the present invention relates to an easily-slidable filmobtained by treating with an organic solvent at least one side of asubstantially amorphous film comprising, as a basic resin, polyarylenethioether having a repeating unit of ##STR2## as a main constituent andnot containing a substantial amount of powdery lubricant, to make thecrystallization degree of its surface layer higher than that of itsinside and then stretching and heat treating the solvent-treated film tomake an arithmetic average surface roughness, Ra, of 2 to 200 nm.

The present invention also relates to the production process thereof.

Hitherto, in the field of electronic and electric products,particularly, film-like products such as magnetic recording materials,capacitor films and insulation films, various kinds of synthetic resinfilms, among all, easily-slidable films have been used in a great amountas base films. Particularly, in the field of heat resistant andeasily-slidable film, polyester films or polyimide films have beenemployed as the base films.

These films have been useful as described above. However, recordingmaterials vapor-deposited with magnetic material or chip capacitors havebeen marketed remarkably in recent years and it has been pointed outthat polyester films are insufficient in its heat resistivity to suchapplications. Accordingly, easily-slidable films having higher heatresistivity have been desired. While on the other hand, there has been aproblem in the polyimide films which are extremely excellent in its heatresistance that they are extremely costly, difficiult for melt formationof film and have large humidity expansion coefficient. Therefore, theyare not suitable for general purposes.

In view of the above, an easily-slidable base film comprisingpolyarylene thioether (hereinafter simply referred to as PATE) has beendisclosed as one of potential candidates for the easily-slidable basefilms which can easily be formed into films by melt processing and havewell balanced properties such as heat resistance, mechanical property,dimensional stability and economical advantage in Japanese PatentApplication Laid-Open (KOKAI) No. 55-34968 (1980). However, as far asthe present inventors recognize, there has been a problem thatpreparation of an easily-slidable base film with small arithmeticaverage surface roughness and without abnormally coarse projections fromthe surface (for example, films for vapor deposition) is difficult bythe disclosed method of adding powdery additives such as calciumcarbonate, since defects or abnormally coarse projections from thesurface of the film are liable to be formed. Further, there is atechnical limit for preparing powdery additives of small size and it isdifficult to disperse such additives of small size uniformly in a filmwith no agglomeration. Furthermore, there has also been a problem in themethod that it is almost impossible to make only one surface slidable.

As a method of producing an easily-slidable film without using powderyadditives, it has also been known to mechanically roughen a film surfaceby pinching with a rough-surface-roll. However, there has been problemsthat it is difficult to prepare an easily-slidable film with a smallarithmetic average surface roughness by such a mechanical method.Therefore, a film prepared by such mechanical method is not suitable forthe use, where an easily-slidable film of particularly small arithmeticaverage surface roughness is required, for instance, applications formagnetic tapes or magnetic floppy discs prepared by vapor deposition.

As a method of producing a PATE base film capable of satisfying bothconditions that only one side can be made easily-slidable and that itsarithmetic average surface roughness is small and substantially noabnormally coarse projections from the surface are present, there may bea method of coating a rough surface layer on a film having a smoothsurface.

However, such a method involves problems that the operation of windingor rewinding the smooth surface film to and from a roll or a machine forthe surface coating is difficult because such films easily sticktogether and that the binders have poor heat resistivities.

The present inventors have made an extensive study for overcoming theforegoing problems and, as a result, have found that an easily-slidablePATE film capable of dissolving the foregoing problems altogether can beobtained by utilizing fine projections of PATE per se formed on the filmsurface instead of using a powdery additive and have accomplished thepresent invention on the basis of such a finding.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a potentiallyeasily-slidable PATE film prepared by treating at least one side of afilm comprising, as a basic resin, PATE having a repeating unit of##STR3## as a main constituent not containing a substantial amount ofpowdery lubricant and being substantially amorphous, to increase thecrystallization degree of the treated surface of the film greater thanthat of its inside, and then applying stretching and heat treatment tothe potentially easily-slidable PATE film for making the easily-slidablefilm having the strength of a predetermined level, the arithmeticaverage surface roughness Ra of the treated surface 2 to 200 nm and thedynamic friction coefficient μk of 0.1 to 0.6.

Still a further object of the present invention is to provide a processfor producing the easily-slidable PATE films described above.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is to illustrate the basic principle of surface rougheningaccording to the present invention.

1. An amorphous layer of an amorphous film

1a. An amorphous layer of the film after the solvent treeatment

1b. An amorphous layer remained after stretching

2. A crystallized layer, coarsely cracked, formed by the solventtreatment

2a. A crystallized layer divided into pieces by stretching

A. Treatment with the solvent

B. Stretching

FIGS. 2(A) and 2(B) are, respectively, electron microscopic photographsshowing the surface of the easily-slidable PATE film according to thepresent invention (FIG. 2A) and the surface of the conventionaleasily-slidable PATE film (FIG. 2B).

DETAILED DESCRIPTION OF THE INVENTION

The easily-slidable PATE film according to the present invention is thefilm obtained by applying stretching, heat treatment, etc. to apotentially easily-slidable film, which comprises a substantiallyamorphous film containing, as a basic resin, PATE having a repeatingunit of ##STR4## as a main constituent and not containing a substantialamount of powdery lubricant and at least the one surface of which isgreater in the crystallization degree than its inside, so that at leastone side of the easily-slidable film has surface properties, i.e.,arithmetic average surface roughness, Ra, in a range of 2 to 200 nm andthe dynamic friction coefficient μk in a range of 0.1 to 0.6. The filmalso has a strength at a break of not less than 15 kg/mm², elongation atbreak of not less than 20%, the tensile modulus of elasticity of notless than 300 kg/mm² and melting point of 260° C. or higher.

Further, the characteristic features of the process for producing theeasily-slidable PATE film according to the present invention comprises(1) treating at least one surface of a film comprising, as a basicresin, PATE having a repeating unit of ##STR5## as a main constituent,not containing substantial amount of powdery lubricant and beingsubstantially amorphous, by at least one organic solvent with asolubility parameter (SP value) in a range of 8.5 to 11.5 or a mixtureof said solvent and water, alcohol type solvent, of aliphatichydrocarbon type solvent, in a liquid or vapor phase, at a temperatureof a solidifying point of the solvent (solvent used alone or as amixture) to 130° C., thereby obtaining a potentially easily-slidablePATE film in which a degree of crystallization of the treated surface ismade higher than that of its inside and (2) subjecting the potentiallyeasily-slidable film to stretching in one or two directions by means ofsimultaneous stretching, of sequential stretching or of both methods ata temperature in a range of 70° to 130° C., at an area factor of 4 to 18and during a time in a range of 1 to 2,000 seconds and, if necessary,further to heat treatment at a temperature in a range of 180° to 280° C.and during a time in a range of 1 to 2,000 seconds.

Further, according to the present invention, all of the foregoingproblems of the conventional easily-slidable films in the prior art havebeen overcome.

Namely, since the present invention does not use powdery lubricant asthe surface roughening material, problems accompanied by its use are notnaturally present and, in addition, since the roughened surface formedon the film is produced by crystallizing only the surface portion of thefilm thereby making the behavior of the surface portion different fromthat of its inside portion, roughening the one surface only can beaccomplished easily. Further, the easily-slidable film according to thepresent invention is produced by a production processes comprising, astep treating the surface with liquid or gas and a stretching step, sothere is no actual problem in practicing.

The easily-slidable PATE film according to the present invention can beused in various applications as it is or as a substrate, on whichmagnetic layer, pigmented layer, plating layer or other layer is formedby means of coating, vapor deposition, etc., namely, base film (later,will be described in detail). In view of the application of PATE film,it can be said that the easily-slidable PATE film according to thepresent invention is particularly useful as a base film on which amagnetic layer is to be applied.

Principle for the Surface Roughening

The surface roughening in the present invention is based on a novelprinciple or idea found by the present inventors, and the properties ofPATE film have been wisely utilized.

Specifically, it has been found that (i) when a surface of an amorphousPATE film is treated by an organic solvent having an adequate affinityto PATE at a much lower temperature than that causing dissolution orswelling of PATE, only the PATE in the film surface portion iscrystallized to reduce the elongation as compared with that of thesubstantially amorphous PATE in its inside portion. As the method ofcrystallizing only a surface portion of a substantially amorphous PATEfilm and reducing the elongation of the surface portion of the filmcompared with that of its inside portion, heat treatment, radiationtreatment, UV-radiation, laser radiation, chemical treatment such asoxidation or the combination thereof can also be included in the presentinvention. It has also been found that (ii) if the film, of which theelongation is reduced only at the surface portion, is stretched, onlythe surface layer is finely divided to cause a sort of radial"micro-wrinkles" at the surface layer and (iii) the "micro-wrinkles"result in a roughened surface for providing high slidability.

The roughened surface thus formed can be understood easily referring tothe schematic cross sectional view (FIG. 1) appended herewith. When anamorphous film only consisting of an amorphous layer 1 is treated with asolvent (A) (on one surface in this case), a coarsely crackedcrystalline layer 2 is formed at the treated surface and when it isstretched (B), a finely cut crystalline layer 2a is formed beingdispersed on the surface of the stretched amorphous layer 1b.

It will be apparent from the electron microscopic observation for thefilm surface that the thus formed roughened surface is quite differentfrom the roughened surface of the conventional easily-slidable filmformed by the addition of powdery lubricant. That is, FIG. 2A shows thesurface of a typical easily-slidable PATE film according to the presentinvention and FIG. 2B shows the surface of a conventionaleasily-slidable PATE film formed by an addition of powdery lubricant,respectively.

Basic Resin

The PATE as the basic resin for the easily-slidable film according tothe present invention means those polymers composed of repeating unit of--Ar--S--(Ar:arylene group) as the constituent.

For the PATE as the starting material of the easily-slidable filmaccording to the present invention, those having p-phenylene group asthe main constituent of arylene group are preferred in respect to thephysical properties such as heat resistance, moldability and mechanicalproperties.

The expression "as the main constituent" in the present invention meansthat the repeating unit of ##STR6## is contained not less than 60 mol %and, preferably, not less than 75 mol % of the total repeating unit of--Ar--S--.

Arylene groups other than p-phenylene group as the main constituentsusable herein can include, for example, m-phenylene group ##STR7##o-phenylene group ##STR8## alkyl-substituted phenylene group ##STR9## inwhich R represents alkyl group, preferably lower alkyl group, and n isan integer from 1 to 4, p,p'-biphenylene-sulfone group ##STR10##p,p'-biphenylene group ##STR11## p,p'-biphenylene ether group ##STR12##p,p'-biphenylene carbonyl group ##STR13## naphthalene group ##STR14##

From the viewpoint of processability, copolymer containing differentkind of repeating units are excellent in most cases than homopolymerconsisting only of the repeating unit of ##STR15## As the copolymer, acopolymer of ##STR16## is preferred. Particularly, those containing therespective repeating unit in a block form, for example, as described inEuropean Patent Application (Laid-Open) No. 166,451 (1986) are preferredto those containing them in a random form, because use of theblock-copolymer is remarkably excellent in physical properties (heatresistance, mechanical property, etc.) while they are substantiallyequal in processability.

As the PATE for the starting material of the film according to thepresent invention, those having substantially linear structure arepreferred in respect to the processability and the physical property ofthe film. However, crosslinked products obtained by using a small amountof crosslinking agent (for example, 1,2,4-trihalobenzene) uponpolymerization within a range not impairing the processability and thephysical property may also be used.

Uncured PATE is preferred for the polymer as the starting material ofthe film according to the present invention. Since cured PATEs containmany branched or crosslinked structures, its use involves variousproblems, in respect to physical properties of the molded products and aprocessability of the composition, such as poor mechanical strength,severe discoloration and low heat statbility upon melt processing.

PATE with the melting point higher than 260° C. is preferable, morepreferable higher than 270° C., for the present invention. If themelting point is lower than 260° C., the major feature as a heatresistant polymer is impaired.

A molecular weight in the suitable range is desirable for the PATE asthe starting material for the easily-slidable film according to thepresent invention. Namely, PATE having a molecular weight correspondingto a range of 0.25 to 0.8 (dl/g), preferably, 0.30 to 0.7 (dl/g)expressed by the inherent solution viscosity n_(inh), in1-chloronaphthalene solution at a concentration of 0.4 (g/dl) at 206° C.PATE with the inherent solution viscosity n_(inh) of less than 0.25(dl/g) is not preferred since it is difficult to prepare aneasily-slidable film as in the present invention and particularly, it isdifficult to prepare a film uniformly stretched in a stretching step.While on the other hand, PATE with the solution inherent viscosityn_(inh) of higher than 0.8 (dl/g) is not preferable from the standpointof fabrication and economical point, since too high melt viscosity makesan extremely high stretching force necessary in the stretching step andaccordingly quite expensive and special equipment becomes necessary inthe step.

The preferable PATE for the present invention can be manufacturedeconomically, for example, by the process described in U.S. Pat. No.4,645,826 filed by the present inventors. In addition, a methoddescribed in U.S. Pat. No. 3,919,177 in which a polymerization aid suchas a carboxylic acid salt is added in a large amount to obtain a highmolecular weight PATE can also be used. However, the latter method isdisadvantageous from an economical point of view.

Easily-Slidable Film According to the Present Invention

Easily-slidable film according to the present invention is a filmcomprising PATE as described above as the basic resin and containing nosubstantial amount of powdery lubricant, used in conventionaleasily-slidable film, such, as, calcium carbonate, silica, clay, kaolineand titanium white. "Containing no substantial amount of powderylubricant" means herein that although such powder is not used as thesurface roughening agent in view of the nature of the present invention,it lies within the scope of the present invention to use a small amountof powdery lubricant with the aim other than that for the surfaceroughening, for example, for adjusting a processability upon meltprocessing.

The potentially easily-slidable PATE film according to the presentinvention comprises a substantially amorphous film in which the degreeof crystallization at least on one surface of the film, is higher thanthat of the inside.

Further, the easily-slidable PATE film according to the presentinvention, has, at least on one surface thereof, the arithmetic averagesurface roughness Ra, that is, center-line average height roughnesswithin a range of 2 to 200 nm, preferably, 5 to 150 nm and the dynamicfriction coefficient μk within a range of 0.1 to 0.6, preferably, 0.2 to0.5.

It is difficult to form an easily-slidable film if the arithmeticaverage surface roughness Ra is less tha 2 nm or greater than 200 nm.Further, the film with the dynamic friction coefficient μk of less than0.1 is very difficult to produce from a PATE film, whereas a film withthe friction coefficient μk in excess of 0.6 is poor in the slidabilityand both films are not preferable.

While on the other hand, it is preferable for the easily-slidable filmaccording to the present invention that it has the strength at break ofnot less than 15 kg/mm², the elongation at break of not less than 20%,the tensile modulus of elasticity of not less than 300 kg/mm² and themelting point of not lower than 260° C. These values for mechanical andthermal properties are particularly required for the applications suchas heat resistant magnetic recording materials, base films, capacitorfilms, insulation films, etc. The easily-slidable film according to thepresent invention has physical properties suitable to theseapplications. Those films having such mechanical and thermal propertiescan be obtained usually by applying stretching and orientation to PATEamorphous films. In other words, it shows that the easily-slidable PATEfilms according to the present invention having such physical propertyvalues are stretched and oriented films. Such physical properties cannot be attained with non-stretched-non-oriented films.

Method of Measuring Physical Properties of Easily-Slidable Film

The respective physical properties of the easily-slidable film accordingto the present invention are measured by the following methods:

Dynamic friction coefficient μk: according to ASTM D-1894; valuesmeasured at 25° C. between films at least one of surface, of which is aroughened surface.

Arithmetic average surface roughness Ra: according to JIS B0601; R_(a)is determined by first generating a roughness curve, expressing theroughness curve as a function, y=f(x), and then calculating R_(a) usingthe following formula: ##EQU1## where l is the measuring length in thedirection of the center line of the reference curve.

Strength at break: according to ASTM D882

Elongation at break: according to ASTM D882

Tensile modulus of elasticity: according to ASTM D882

Melting point: Differential Scanning, Calorimetry (DSC) method

Preparation of Easily-Slidable Film

The preparation process for the easily-slidable PATE film according tothe present invention comprises treating an amorphous PATE film with aspecific organic solvent and applying stretching and heat setting and incase of necessity, heat relaxation.

In addition, as a method of crystallizing only the surface of asubstantially amorphous PATE film thereby reducing the elongation at thesurface as compared with that of the inside, heat treatment, radiationtreatment, UV radiation, laser radiation, chemical treatment such asoxidation or combinations thereof should not be excluded from the scopeof the present invention.

(1) Preparation of amorphous film

A film suitable, as an amorphous PATE film, for use in the presentinvention, can be prepared by melt-extruding PATE described above at atemperature not lower than the melting point and not higher than 400°C., and then quenching on a cooling drum or in a cooling medium such aswater to a temperature not higher than its secondary transition point.

In the present invention, the amorphous film means those substantiallyamorphous films, for example, with the degree of crystallization(measured by a density method) of less than about 10%. The densitymethod herein means such a method of drying a sample under a reducedpressure till it reaches a constant weight, then measuring the densityby using a density gradient tube and then calculating the degree ofcrystallization based on the measured value (provided that the densityof PATE at the crystallized portion of 1.43 and the density at theamorphous portion of 1.32 were used for the calculation).

(2) Treatment with organic solvent

The production process for the easily-slidable film according to thepresent invention comprises at first treating the surface of anamorphous PATE film with an organic solvent. This treatment can providea potentially easily-slidable film, which can further be applied withstretching and heat treatment to get an easily-slidable film.

The temperature for the treatment is within a range of the solidifyingpoint of the solvent up to 130° C., and the organic solvent serves tocrystallize only the surface layer of the amorphous film to reduce theelongation thereof. Accordingly, it is not a so-called "etching" effectof dissolving and leaching the amorphous film with the solvent.

While the PATE film can be crystallized also by heat treatment, it isextremely difficult to crystallize thereby only the surface layerselectively. While on the other hand, it is assumed that by the organicsolvent treatment according to the present invention in which only thesurface of the film is exposed to liquid or vapor of the solvent havingan adequate affinity with PATE, the molecule of the solvent intrudesinto the PATE film to the surface layer and can selectively crystallizeonly the surface layer by an effect, so to speak, like molecular rolls.Accordingly, the surface layer of the film can easily be crystallizedeven at a temperature not higher than the secondary transition point ofPATE. While on the other hand, excess temperature for the solventtreatment is not preferred since the crystallized layer formed at thePATE surface is dissolved or leached out.

For the organic solvent used in the step of the organic solventtreatment for the amorphous PATE film according to the presentinvention, those solvents having appropriate affinity with PATE arepreferred. They are used in the form of liquid or, depending on thecase, vapor thereof.

Regarding the affinity between PATE and solvent, a SP value (solubilityparameter) generally gives an effective measure.

For the purpose according to the present invention, aliphatichydrocarbons of low SP value and water, alcohols, amines, etc. ofexcessively high SP value or high hydrogen bonding strength are notpreferred.

Accordingly, organic solvents of SP value of 8.5 to 11.5, preferably, of9 to 11 are preferred as the solvent for use in the present invention.

As the organic solvent applied to the treatment for increasing thedegree of crystallization at the surface of the film according to thepresent invention, there can be mentioned the solvents having SP valueof 8.5 to 11.5 among the followings: ethers such as tetrahydrofuran anddioxane, etc.; organic amides such as dimethylacetoamide,dimethylformamide, N-methylpyrrolidone, dimethylimidazolidinone,tetramethyl urea, hexamethyl phosphoric triamide, etc.; halogenatedhydrocarbons such as chloroform, trichlene, dichloromethane,perchloroethylene, ethylene dichloride, bromobenzene, etc.; carbondisulfide; ketones such as acetone, methyl ethyl ketone andcyclohexanone, etc.; thioethers such as diphenyl thioether, etc.;aromatic hydrocarbons such as toluene, etc.; esters such as ethylacetate, etc.; nitro compounds such as nitrobenzene, etc.; pyridines orquinolines; cyano compounds such as cyanobenzene, etc.; and sulfonessuch as sulforan, etc. They may be used alone or as a solvent mixture oftwo or more of them. Among them, ethers, organic amides and halogenatedhydrocarbons are particularly preferable since they have properly higheffect. On the other hand, it is somewhat difficult to use carbondisulfide since the effect is too strong. Although, water, alcohols andaliphatic hydrocarbons have no substantial effect, they may be used asthe diluent for the above organic solvents. Details for the SP value aredisclosed, for example, in "Polymer", 13,285 p (1972) and the disclosurethereof is to be referred to, when it becomes necessary in the presentinvention.

The temperature for the organic solvent treatment is preferably higherthan the solidifying point of the organic solvent used and not higherthan 130° C., particularly, within a range of 0° C. to 100° C. Thetemperature lower than the solidifying point is not preferred since nosubstantial crystallization occurs at the surface layer. While on theother hand, temperature in excess of 130° C. is not preferred since thecrystallization of inside of the film is also promoted.

The solvent treatment for the amorphous film in the production processof the easily-slidable film according to the present invention isapplied for selectively crystallizing only the surface layer of the filmthereby reducing the elongation of the surface layer. However, if thecrystallized layer is too thick, it is not preferable since breakage ofthe film occurs upon stretching. As the index expressing the extent ofthe solvent treatment to get a potentially easily-slidable film, thearithmetic average surface roughness Ra for the solvent-treated filmbefore stretching can be used. This Ra value is usually differentconsiderably from the Ra value for the easily-slidable film obtainedafter stretching and heat setting.

In the present invention, it is preferable that the organic solventtreatment is applied so that Ra for the solvent-treated potentiallyeasily-slidable film before stretching is within a range of 10 to 150nm, more preferably, within a range of 15 to 130 nm. Ra value of lessthan 10 nm is not preferable since it is difficult to reduce the dynamicfriction coefficient of the film obtained after stretching to less than0.6. While on the other hand, if the solvent treatment is applied tillRa exceeds 150 nm, it is not preferable because the crystallized layerusually becomes too thick thereby possibly causing breakage of the filmin the stretching step.

It is preferable that the organic solvent treatment is conducted so thatRa for the solvent treated film reaches an adequate value within a rangeof 10 to 150 nm under a sufficient temperature and time. Although theadequate treating time therefor varies depending on the factors such asthe kind of the solvent used, the extent of its dilution and thetreating temperature, usually it is preferable that the time is in therange of 0.1 to 1,000 seconds, more preferable 0.5 to 500 seconds.Treating time of less than 0.1 second is not preferred since the controlfor the treating time is extremely difficult. While on the other hand,treating time in excess of 1,000 seconds is not preferred in respect toindustrial productivity and an economical point, since the productivityof the easily-slidable film is remarkably reduced.

The organic solvent and the amorphous film may be brought into contactwith each other by means of an optional method along with the purpose.Immersion of a film into a solvent, coating of a solvent to the surfaceof the film, exposure of the surface of the film to the vapor of thesolvent, etc. are generally preferred. The preferable controlling methodof the time of contact is by washing off or diluting the solventdeposited on the surface with liquid such as alcohol or aliphatichydrocarbon at a predetermined time after the contact, or by evaporatingor removing the solvent by means of heating or pressure reduction at apredetermined time after the contact. From the standpoint of easyremoval of the solvent the boiling point of the solvent for use in thesurface treatment is preferably not higher than 150° C., morepreferably, not higher than 100°.

(3) Stretching

Stretching is preferably conducted to the potentially easily-slidablefilm, by applying stretching in one direction or simultaneous and/orsequential stretching in two directions with or without preheatingwithin such a range of temperature as the crystallization of the filmdoes not progress, at a range of stretching temperature 70° to 130° C.,preferably, 80° to 120° C. within an area stretching factor from 4 to 18times, preferably, 8 to 16 times by using an adequate device, forexample, rolls or tenters.

Stretching temperature lower than 70° C. is not preferred since the filmmay be broken. While on the other hand, the temperature in excess of130° C. is not preferred since coarse spherulites may be formed and thefilm becomes white. If the area stretching factor is less than 4 times,it is not preferred since coarse spherulites may be formed to result inwhitening or forming wrinkles in the subsequent heat setting step. Onthe other hand, the stretching factor in excess of 18 times is notpreferred since the film probably be broken.

By applying the stretching, mechanical and thermal properties of thefilm can be improved and an appropriately roughened surface can beformed on the film surface thereby obtaining the easily-slidable film ina higher level.

(4) Heat treatment

(i) Heat setting

The film stretched to orient in one direction or two directions issubjected to heat setting at a heat setting temperature within a rangeof 180° to 280° C., preferably, 200° to 270° C., for a heat setting timewithin a range of 1 to 2,000 seconds, preferably, 5 to 1,000 seconds. Ifthe heat setting temperature is lower than 180° C., improvement in theheat resistance of the film can be insufficient and is not preferable.While on the other hand, if the temperature is in excess of 280° C.,film may undesirably be melted again. Further, if the heat setting timeis less than 1 second, improvement in the heat resistance of the filmmay be insufficient. While on the other hand, if it exceeds 2,000seconds, the film may be degraded thermally or the productivity may bereduced remarkably. All these cases are not preferable either.

By the heat setting treatment, the heat resistivity of the film can beimproved and, in addition, the roughened surface formed in thestretching step can be stabilized.

(ii) Heat relaxation

The film after subjected to the stretching and heat setting may furtherbe applied with heat relaxation in case of necessity. That is, heatrelaxation is conducted at a heat treating temperature within a range of180° to 280° C., more preferably, 200° to 270° C., for a heat treatingtime within a range of 1 to 2,000 seconds, preferably, 5 to 1,000seconds.

If the heat relaxation temperature is lower than 180° C., the heatrelaxation effect for the film may become insufficient. While on theother hand, if it exceeds 280° C., the film may possibly be meltedagain. Further, if the heat relaxation time is less than 1 second, theheat relaxation effect probably becomes insufficient. While on the otherhand, if it exceeds 2,000 seconds, the film may thermally be degraded orthe productivity is reduced remarkably.

By the heat relaxing treatment, dimensional stability of the film athigh temperature can be improved.

Application of the Film According to the Present Invention

The easily-slidable PATE film according to the present invention is aneasily-slidable film with no requirement of powdery lubricants, whichhas less defects, can be controlled in the surface roughness relativelyeasily, is excellent in the mechanical properties and has heatresistance and moisture proofness superior to those of polyester filmsand, accordingly, it can be applied generally as base films for highperformance magnetic recording material (particularly for vapordeposition type, etc.), as well as for base films for use as highperformance capacitor films (particularly, chip capacitor, etc.),insulation films, printer tapes, photographic films, etc. Furthermore,the film according to the present invention having higher surfaceroughness also has advantageous features of easy plating, printing orbonding and, accordingly, it is suitable for printed wiring substrates,printing films, coating film, etc.

EXPERIMENTAL EXAMPLE

The present invention will now be described specifically in thefollowing experimental examples by way of specific examples but theinvention is no way restricted only thereto.

SYNTHESIS EXAMPLE 1

Into an autoclave lined with titanium, 64.5 kg of hydrous sodium sulfide(solid content: 46.12%) and 163.5 kg of N-methylpyrrolidone (NMP) werecharged and temperature was elevated to about 203° C. to distill out 32kg of water. 1.2 kg of water and 49.5 kg of NMP were additionallysupplied (total water content/NMP=2.4 mol/kg). Then, 60.5 kg ofm-dichlorobenzene was charged (total arylene group/NMP=1.9 mol/kg).

Polymerization was conducted under the conditions at 230° C./2 hours and235° C./8 hours to obtain a slurry M-1 containing the resultant(m-phenylene thioether)prepolymer.

While on the other hand, 304.6 kg of hydrous sodium sulfide (solidcontent: 46.12%) and 820 kg of NMP were charged in an autoclave linedwith titanium and temperature was elevated to about 203° C. to distillout 116 kg of water. 1 kg of water and 52 kg of NMP were additionallysupplied (total water content/NMP=3.0 mol/kg). Then, 259 kg ofp-dichlorobenzene was charged (total arylene group/NMP=2.0 mol/kg).

Reaction was conducted under the condition at 215° C./10 hours. Then,72% of the slurry M-1 and 151 kg of water were added and polymerizedunder the condition at 260° C./5 hours to obtain a slurry containing theresultant block copolymer.

The resultant slurry was sieved through a screen of 0.1 mm mesh toseparate only the granular polymer, which was washed with acetone andthen with water to obtain a cleaned polymer. The cleaned polymer wasdried at 80° C. under a reduced pressure to obtain a polymer A. Thesolution inherent viscosity n_(inh) of the polymer A (in1-chloronaphthalene solution at 0.4 g/dl concentration at 206° C.,hereinafter, the viscosity is measured under this condition) was 0.38(dl/g).

SYNTHESIS EXAMPLE 2

Into an autoclave lined with titanium, 371 kg of hydrous sodium sulfide(solid content: 46.27%) and 1,028 kg of NMP were charged and temperaturewas elevated to about 203° C. to distill out 143 kg of water. 4 kg ofwater and 45 kg of NMP were additionally supplied (total watercontent/NMP=3.0 mol/kg). Then 318 kg of p-dichlorobenzene was charged(total arylene group/NMP=2.0 mol/kg).

Polymerization was further conducted under the condition at 220° C./5hours and then 96.5 kg of water was additionally supplied (total watercontent/NMP=8.0 mol/kg).

Polymerization was conducted under the condition at 256° C./2 hours and244° C./9 hours to obtain a slurry containing the resultant polymer.

The slurry was sieved through a screen of 0.1 mm mesh to separate onlythe granular polymer, which was washed with acetone and then water toobtain a cleaned polymer. The cleaned polymer was dried at 80° C. undera reduced pressure to obtain a polymer B. The solution inherentviscosity n_(inh) of the polymer B was 0.43 (dl/g).

SYNTHESIS EXAMPLE 3

Into an autoclave lined with titanium, 427 kg of hydrous sodium sulfide(solid content: 45.70%) and 925 kg of NMP were charged and temperaturewas elevated to about 203° C. to distill out 173 kg of water. 3.5 kg ofwater and 51.5 kg of NMP were additonally supplied (total watercontent/NMP=3.5 mol/kg). Then, 374 kg of p-dichlorobenzene was charged(total arylene group/NMP=2.6 mol/kg).

Polymerization was conducted under the condition at 220° C./5 hours and61.5 kg of water was additionally supplied (total water content/NMP=7.0mol/kg). Polymerization was conducted under the condition at 255° C./5hours to obtain a slurry containing the resultant polymer.

The resultant slurry was sieved through a screen of 0.1 mm mesh toseparate only the granular polymer, which was washed with acetone andthen with water to obtain a cleaned polymer. The cleaned polymer wasdried at 80° C. under a reduced pressure to obtain a polymer C. Thesolution inherent viscosity n_(inh) of the polymer C was 0.22 (dl/g).

AMORPHOUS FILM PREPARATION EXAMPLE 1

Part of each polymers A, B and C obtained as described above wassupplied to an extruder, melted at 320° C., extruded into a strand-likeshape, rapidly cooled with water and cut to pieces and pellets A, B andC were prepared. Each of the pellets A, B and C was respectivelysupplied to an extruder, melted at 320° C., extruded through a T diehaving a linear lip and then cast on a metal drum to cool and solidify.During the extrusion, to a pinning wire which was stretched in parallelwith the drum axis apart by about 0.5 cm from the position where theextruded molten product was in contact with the drum, static electricityof 7 KV was applied. The resultant amorphous films A, B and C had athickness of 150 μm and density of 1.324 g/cm³, 1.323 g/cm³ and 1.325g/cm³, respectively.

AMORPHOUS FILM PREPARATION EXAMPLE 2

Kaolin powder of 300 nm in average diameter was added by 0.1 (PHR) to aportion of the polymer A obtained as described above and blended in amixer to prepare an amorphous film (A2) in the same manner as inPreparation Example 1. The amorphous film (A2) had a thickness of about150 μm and the density of 1.325 g/cm³.

PREPARATION EXAMPLES 1-20 FOR EASILY-SLIDABLE FILMS

Amorphous films A, B, C and A2 obtained as described above weresubjected to treatment while varying the organic solvent, temperatureand treating time as shown in Table 1 and, directly after the treatment,immersed in methanol to remove the treating solvent and then air dried.

The air-dried product was stretched to orient at 99° C. by 3.5 times inone direction and by 3.5 times in the direction of the right anglethereto sequentially by using a small size film stretcher (manufacturedby T. M Long Co.) to prepare stretched film. Those stretched films notbroken during stretching were set to a metal frame and applied with heatsetting treatment at 263° C./5 minutes. The resultant heat set film wasdetached from the frame and applied with heat relaxation in a free stateat 257° C./2 minutes.

The surface roughness and the dynamic friction coefficient were measuredfor the air-dried films and stretched, heat-set and heat relaxed filmsobtained therefrom according to JIS B-0601 and ASTM D 1894 (25° C.)respectively. Number of abnormally coarse projections greater than 200nm was also determined together with the measurement for the surfaceroughness. These results are shown collectively in Tables 1 and 2.

                                      TABLE 1                                     __________________________________________________________________________           Solvent treatment                                                                 Solvent           Stretched, heat set film property                Exp.   treated                                                                           (wt.  Temp.                                                                             Time                                                                              Ra  m.p.            Ra     μk                     No.                                                                              Film                                                                              surface                                                                           ratio)                                                                              (°C.)                                                                      (sec)                                                                             (nm)                                                                              (°C.)                                                                     *1) *2) *3)  (nm)                                                                              *4)                                                                              *5)                                                                              Remark                 __________________________________________________________________________    1  A   --  --    --  --  --  277                                                                              26/25                                                                             70/80                                                                             380/380                                                                             5  0  >1 Comp. Ex. *6)          2  B   --  --    --  --  --  280                                                                              27/26                                                                             60/70                                                                             390/380                                                                             6  0  >1 Comp. Ex. *6)          3  A   single                                                                            THF/ac-                                                                             24  5   20  277                                                                              25/24                                                                             65/75                                                                             370/360                                                                            30  0  0.3                                  etone                                                                         (85/15)                                                            4  B   single                                                                            THF/ac-                                                                             24  5   15  280                                                                              24/23                                                                             60/70                                                                             380/360                                                                            25  0  0.3                                  etone                                                                         (85/15)                                                            5  C   single                                                                            THF/ac-                                                                             24  5   25  -- --  --  --   --  -- -- Comp. Ex. *7)                     tone                                                                          (85/15)                                                            6  A2  single                                                                            THF/ac-                                                                             24  5   30  278                                                                              19/18                                                                             70/90                                                                             320/350                                                                            40  9  0.4                                                                              Comp. Ex. *8)                     etone                                                                         (85/15)                                                            7  B   both                                                                              diox- 60  2   20  277                                                                              20/20                                                                             80/90                                                                             350/350                                                                            30  0  0.4                                  ane                                                                8  A   both                                                                              chloro-                                                                             25  2   25  280                                                                              23/22                                                                             65/70                                                                             350/330                                                                            40  0  0.3                                  form                                                               9  B   both                                                                              NMP   25  2   90  277                                                                              17/16                                                                             40/60                                                                             320/310                                                                            140 0  0.5                       10 A   both                                                                              DMC   40  2   20  277                                                                              24/24                                                                             70/75                                                                             370/350                                                                            30  0  0.4                       __________________________________________________________________________     In this Table, THF means tetrahydrofuran and DMC means dimethyl acetamide     *1): Strength at break (kg/mm.sup.2)                                          *2): Elongation at break (%)                                                  *3): Tensile modulus of elasticity (kg/mm.sup.2)                              *4): Number of abnormally coarse projection larger than 200 nm                *5): μk in the column indicated by "single" in the line of "treated        surface" represents a value between a solvent treated surface and a           nottreated surface, while μk in the column indicated by "both"             represents a value between solvent treated surfaces                           *6): Without solvent treatment.                                               *7) Broken at stretching.                                                     *8) Many abnormally coarse projections.                                  

                                      TABLE 2                                     __________________________________________________________________________           Solvent treatment                                                                 Solvent           Stretched, heat set film property                Exp.   treated                                                                           (wt.  Temp.                                                                             Time                                                                             Ra   m.p.             Ra    μk                     No.                                                                              Film                                                                              surface                                                                           ratio)                                                                              (°C.)                                                                      (sec)                                                                            (nm) (°C.)                                                                     *1) *2)  *3)  (nm)                                                                             *4)                                                                              *5)                                                                              Remark                 __________________________________________________________________________    11 B   both                                                                              *6)   60  2  20   280                                                                              19/18                                                                             80/90                                                                              340/320                                                                            40 0  0.4                       12 A   both                                                                              *7)   25  2  25   277                                                                              22/20                                                                             80/95                                                                              350/320                                                                            25 0  0.5                       13 B   both                                                                              *8)   25  2  20   280                                                                              23/23                                                                              90/100                                                                            340/320                                                                            35 0  0.5                       14 A   both                                                                              *9)   24  2  30   277                                                                              20/17                                                                             90/95                                                                              320/320                                                                            40 0  0.5                       15 A   single                                                                            NMP   80  5  >200 -- --  --   --   -- -- -- Comp. Ex. *11)         16 B   single                                                                            CS.sub.2                                                                            25  5  >200 -- --  --   --   -- -- -- Comp. Ex. *11)         17 B   single                                                                            water 40  30  6   280                                                                              26/26                                                                             70/80                                                                              390/370                                                                             7 0  >1 Comp. Ex.              18 A   both                                                                              meth- 25  30  7   277                                                                              26/25                                                                             80/80                                                                              390/380                                                                             7 0  >1 Comp. Ex.                         anol                                                               19 A   both                                                                              hexane                                                                              25  30  8   277                                                                              26/24                                                                             70/90                                                                              380/360                                                                             8 0  >1 Comp. Ex.              20 B   both                                                                              *10)  204 5  --   -- --  --   --   -- -- -- Comp. Ex.              __________________________________________________________________________                                                           *12)                    In this Table, NMP means Nmethylpyrrolidone.                                  *1): Strength at break (kg/mm.sup.2)                                          *2): Elongation at break (%)                                                  *3): Tensile modulus of elasticity (kg/mm.sup.2)                              *4): Number of abnormally coarse projection larger than 200 nm                *5): μk in the column indicated by "single" in the line of "treated        surface" represents a value between a solvent treated surface and a           nottreated surface, while μk in the column indicated by "both"             represents a value between solvent treated surfaces                           *6): Dioxane/toluene (80/20)                                                  *7): CS.sub.2 /NMP/pyridine (10/60/30)                                        *8): Nitrobenzene/trichlene (20/80)                                           *9): Ethylacetate/tetrahydrofuran (10/90)                                     *10): 1Chloronaphthalene                                                      *11): Broken at stretching                                                    *12): Film was partially dissolved and remarkably deformed               

PLATING EXAMPLE

Films of Comparative Example and according to the present inventionobtained in Preparation Examples 2 and 9 for easily-slidable films wereapplied with chemical copper plating as described below.

(i) Catalyzing treatment:

Both of the films were subjected to immersion in a catalyzing solutionof 100 ml in total volume comprising 0.020 g PdCl₂ /0.2 g SnCl₂ /10 mlHCl/water for 10 minutes respectively.

(ii) Water washing:

The resultant catalyzed film were washed with deionized water.

(iii) Chemical copper plating treatment:

The washed films were subjected to immersion in a plating solution of100 ml of total volume containing 1.56 g CuSO₄.5H₂ O/1.0 g NaOH/5.0 gNaKC₄ H₄ O₆.4H₂ O/1.0 ml 37% formalin/water at 0° C. for 20 minutes.

(iv) Water washing:

The plated films were sufficiently washed with deionized water and airdried.

Among the resultant copper plated films, plating metal was firmlyadhered on the plated films obtained from the film according to thepresent invention, whereas plated metal was easily defoliated even byslight rubbing on the plated films obtained from the film of theComparative Example.

What is claimed is:
 1. A process for producing an easily-slidablepolyarylene thioether film having an arithmetic average surfaceroughness, Ra, in a range of 2-200 nm and a dynamic frictioncoefficient, μk, within a range of 0.1-0.6 at least on one surface ofthe film, which comprises:a) contacting at least one surface of anamorphous film, containing the polyarylene thioether, consistingessentially of repeating units of the formula: ##STR17## with at leastone organic solvent having a solubility parameter within a range of8.5-11.5, and being selected from the group consisting of ethers,thioethers, organic amides, halogenated hydrocarbons, carbon disulfide,aromatic hydrocarbons, pyridines, quinolines, nitro compounds, ketones,esters, cyano compounds and sulfones; or a mixture of any of the abovesolvents with water, alcohols or aliphatic hydrocarbons; until thearithmetic surface roughness, Ra, of the contacted film reaches 10-150nm, thereby increasing a degree of crystallization at the surface of thefilm which is higher than that of the inside; b) stretching thecontacted film at a temperature within the range of 70°-130° C. and atan area stretching factor of 4-18 times; and c) heat setting thestretched film at a temperature within the range of 180°-280° C. for atime within a range of 1-2000 seconds.
 2. The process according to claim1, wherein the film produced by the process has a strength at break ofnot less than 15 kg/mm², an elongation at break of not less than 20%, atensile modulus elasticity of not less than 300 kg/mm² and a meltingpoint of not lower than 260° C.
 3. The process according to claim 1,wherein said process further comprises d) heat relaxing said heat setfilm at a temperature within a range of 180°-280° C. for a time within arange of 1-1,000 seconds.
 4. The process according to claim 1, wherein asolution inherent viscosity, n_(inh), in 1-chloronaphthalene solution ata concentration of 0.4 g/dl at 206° C. of the polyarylene thioethercontained in said amorphous film is in the range of 0.25-0.8 dl/g.